PRODUCTION OF EXOGENOUS GONADOTROPIN-NEUTRALIZING IMMUNOGLOBULINS IN CATS AFTER REPEATED ECG-HCG TREATMENT AND RELEVANCE FOR ASSISTED REPRODUCTION IN FELIDS

Combination regimens of equine chorionic gonadotrophin (eCG) and human chorionic gonadotrophin (hCG) are used in ovarian stimulation protoco ls for assisted reproduction of felids. In the present study, domestic cats exhibited decreased ovarian responsiveness after repeated admini stration of eCG-hCG and a possible immunological mechanism for this ov arian refractoriness was investigated. An ELISA was used to analyse se ra from male, naive female and previously eCG-hCG-stimulated (1x, 3x a nd 4x) female cats for the presence of immunoglobulins binding to eCG, hCG and pig FSH (pFSH). The sera of cats receiving multiple eCG-hCG i njections, at intervals of 44-50 days, displayed greater eCG and hCG-b inding than did the sera of male, naive female or female cats stimulat ed once, and demonstrated variable affinity for pFSH. In preovulatory and postovulatory ovarian stimulation assays, mice injected with an eC G-antisera mixture had lower ovary masses than did mice injected with eCG-saline and fewer ovulated oocytes compared with mice treated with eCG-naive sera. Treatment of queens that were refractory to eCG-hCG wi th a pFSH-hCG regimen caused a rebound in development of ovarian folli cles but not in oocyte maturity. These studies indicated that repeated treatment of domestic cats with eCG and hCG may cause an immunologica lly mediated refractoriness to ovarian stimulation. Although alternati ve gonadotrophin regimens may alleviate this refractoriness, a prefera ble strategy might be the avoidance of potential immunological complic ations through the cautious use of eCG and hCG in domestic and endange red nondomestic felids.